1. Field
The present embodiments generally relate to processes for upgrading of heavy oils and bitumens. More particularly, the present embodiments relate to processes for the upgrading of heavy oils and bitumens including one or more of the steps of production, fractionation, solvent extraction, fluid catalytic cracking and hydrotreating to produce synthetic crude and/or naphtha, distillate and gas oil streams having reduced metal and/or sulfur content.
2. Description of the Related Art
As world reserves of light, sweet crudes diminish and worldwide consumption of oil increases, refiners seek methods for extracting useful oils from heavier crude resources. The heavier crudes, which can include bitumens, heavy oils and tar sands, pose processing problems due to significantly higher concentration of metals, most notably nickel and vanadium. In addition, the heavier crudes typically have higher sulfur and asphaltene content, posing additional problems in the upgrading of crudes. Finally, tar sands, bitumens and heavy oils are extremely viscous, resulting in problems in transporting the raw materials by traditional means. Heavy oils and bitumens often must be maintained at elevated temperatures to remain flowable, and/or mixed with a lighter hydrocarbon diluent for pipeline transportation. The diluent can be expensive and additional cost can be incurred in transporting it to the location where production is occurring.
As the prices of light oil and natural gas continue to increase, the price of heavy oils and bitumens remains relatively low due to the difficulty in the recovery and upgrading to useable oils. The recovery of bitumens and other heavy crudes is expensive due to substantial energy requirements in the production.
Extensive reserves in the form of “heavy crudes” exist in a number of countries, including Western Canada, Venezuela, Russia, the United States, and elsewhere. These deposits of heavy crudes often exist in areas that are inaccessible by normal means. Generally, the term “heavy crude” refers to a hydrocarbon material having an API gravity of less than 20. Typical heavy crude oils are not fluid at ambient temperatures, and contain a high fraction of materials boiling above 343° C. (650° F.) and a significant portion with a boiling point greater than 566° C. (1050° F.). The high proportion of high boiling point hydrocarbons materials typical in heavy oils make fractionation difficult without resorting to vacuum fractionation.
High metals content in the hydrocarbon feed presents similar processing difficulties. Metals and asphaltenes in the heavy hydrocarbon materials are undesirable in the separated oil fractions as the metals tend to poison catalysts conventionally used in upgrading the oil fractions to other useful products. Asphaltenes will tend to foul/plug downstream equipment. Because of such difficulties during processing by conventional methods, the highest boiling portions are often thermally upgraded by coking or visbreaking processes. The heaviest fractions of heavy oil and bitumen containing the bulk of the metal and asphaltene can be separated by fractionation to recover lighter oils, which can be upgraded catalytically. However, the heavier fraction is still left with some usable oils that can not be extracted using fractionation techniques.
Metals present in heavy oils can include, for example, vanadium and nickel. Vanadium is typically present in excess of 100 wt ppm, often greater than 200 wt ppm. Nickel is typically present in excess of 50 wt ppm, with 75 wt ppm and greater also common.
Solvent extraction of the residuum oil has been known since the 1930's, as previously described in U.S. Pat. No. 2,940,920, to Garwin. With the introduction of the commercially available ROSE® process technology, solvent deasphalting processes have become more efficient and cost effective. Solvent deasphalting technology is commonly used today as one method of bottom-of-the-barrel upgrading in a deep conversion refinery and can also be used to produce fluid catalytic cracker (FCC) feeds, lube bright stocks, deasphalted gas oil feeds for hydrotreating and hydrocracking units, specialty resins, and heavy fuel and asphalt blending components from heavy oil feedstocks. Improved techniques in solvent extraction have been disclosed in U.S. Pat. No. 5,843,303 to Ganeshan.
Prior studies have focused on methods of increasing the transportability of heavy crudes by decreasing their viscosities. U.S. Pat. No. 5,192,421 to Audeh et al., discloses an improved method of demetallization during the deasphalting process, including the steps of deasphalting heavy asphalt-rich crudes, followed by thermal treatment, to produce deasphalted crude having a reduced metal content.
In U.S. Pat. No. 4,875,998, Rendall discloses the extraction of bitumen oils from tar-sands with hot water. Specifically, bitumen oils are conditioned in hot water and then extracted with a water immiscible hydrocarbon solvent to form a mixture which settles into several phases. Each phase can be processed to produce product bitumen oils and recycled process components. Other water or solvent extraction processes are disclosed in U.S. Pat. No. 4,160,718 to Rendall; U.S. Pat. No. 4,347,118 to Funk, et al.; U.S. Pat. No. 3,925,189 to Wicks, III; and U.S. Pat. No. 4,424,112 to Rendall. All patents and publications referenced to herein are hereby incorporated by reference in their entireties.
A need, therefore, for more efficient processes for upgrading of heavy oils and bitumens.